Since its invention, plastic tubing has increasingly been used in residential, commercial and industrial applications that were previously the domain of brass, copper and steel tubing. Plastic tubing offers many advantages over its metal predecessors. Plastic tubing is extremely flexible allowing for quick and easy installation as compared to metal tubing. In the case of demanding applications, the wide variety of available plastic polymers allows a user to select chemically inert and resistant tubing to meet the unique requirements of their application. Finally, nearly anyone can install plastic tubing as it does not require the skill set that typical metal tubing installations require.
A variety of methods have been developed for creating joints with plastic tubing. Most methods involve mechanical couplings providing temporary connections. Because the typical mechanical connection functions only due to a temporary mechanical seal, the potential for leaking is present when using such connections. Examples of these types of mechanical connections include the use of ferrules with a crimp process, push-style fittings such as those manufactured by John Guest International Ltd. and threaded style compression fittings such as those manufactured by JACO Manufacturing Company.
When users confront demanding applications, users typically select the appropriate tubing based on the polymer which best provides characteristics for their application. Many users will select specialty plastic polymers such as Polyvinylidene Fluoride (PVDF), Teflon® and cross-linked Polyethylene (PEX) when the demands of the application requires concern for chemical compatibility or elevated temperature issues. Unfortunately, many of the characteristics which make the use of specialty plastics desirable also lead to difficulties when a user attempts to create tubing joints. Subsequently, the user's ability to create permanent, leak-proof joints with these specialty plastics exceeds the problems associated with more standard polymers such as nylon, polyethylene and polypropylene.
An example of the types of problems associated with creating permanent, leak-proof joints is demonstrated by PEX tubing. There are several methods of manufacturing PEX. The fundamental result is that the molecular chains of polyethylene are cross-linked, resulting in a polymer that shows strength and durability over a wide temperature range. Unfortunately, this strength and durability prevents PEX from exhibiting the chemical and adhesive bonding traits that are common with other polymers. Because of this limitation, a variety of mechanical means for creating joints with PEX tubing have been developed. These means typically include crimping means and metal tubing inserts.
An example of such mechanical means include the Vanguard CRIMPSERT™ metallic insert fitting. The CRIMPSERT™ fitting uses insert fittings and crimp rings made of copper or brass. Using a crimping tool, the user is able to mechanically seal the joint.
Another example of such mechanical sealing means includes the Wirsbo ProPEX® fitting system. The ProPEX® system uses the shaped-memory characteristic of PEX. An expander tool is used to expand an end of the PEX tubing. An insert fitting is inserted into this expanded tubing and the expander tool is then removed. The tubing returns to its original shape, thereby compressing and holding the insert fitting in place.
What is required is a joint forming technique for plastic tubing, especially tubing constructed of specialty plastic polymers, allowing for quick, repeatable and permanent connection of plastic tubing joints.